The present invention relates to electronic proximity switches, and in particular to an electronic proximity switch which is highly resistant to mechanical and electrical noise and to temperature changes.
Electronic proximity switches may detect the presence of an object, for example, a human hand near a switch plate, to provide an electrical signal that may be used to switch a circuit or activate a mechanism. Unlike a typical mechanical switch, an electronic proximity switch does not require moving parts, such as a button or switch operator, that may wear or break. Because an electronic proximity switch may activate at a distance, it can be more readily sealed against environmental contamination and protected from damage. Further, activation at a distance allows the switch to be activated rapidly without careful hand placement or the need for one's fingers to be free to press a button or the like.
A significant problem with electronic proximity switches is their susceptibility to unintended triggering. This can occur in electronic proximity switches that are used outdoors, such as with automotive door lock applications, where there is a risk that rain or debris carried in the wind could activate the switch. Further, the sensitive electronics of the electronic proximity switch often can be triggered by electromagnetic interference, for example, from electrical appliances, radio transmitters, or lightning discharge. The circuitry of electronic proximity detectors, which must measure small changes in electrical fields, can be sensitive to drift in the value of electronic components of the circuitry caused by aging or changes in temperature. Steps to avoid these problems can increase the complexity and cost of the electronic proximity switch, rendering it impractical for many consumer applications.